Electrolytic etching



Sept. 5, 1939.

F. J. BRISLEE ET AL ELECTROLYTIC ETCHING Filed Feb. 10, 1938 5 Sheets-Sheet l RA/vc/s JOSEPH ems/.5: no RE INALD BL/acKeuR/v Sept. 5, 1939- I I F. J. BRISLEE ErAL 2,172,158

ELECTROLYT IC ETCHING Filed Feb. 10, 1938 3 Sheets-Sheet 2 BY w miw Patented Sept. 5, 1939 PATENT OFFICE,

ELECTROLYTIC ETCHING Francis Joseph Brislee, Huyton, and Reginald Blackburn, Prescot, England, assignors to British Insulated Cables Limited, Prescot, England,

a British company Application February 10, 1938, Serial No. 189,796 In Great Britain June 11, 1935 7 Claims.

This inevntion deals with electrolytic etching of zinc and other metal plates for the production of printing surfaces and for other purposes. This application is a continuation-in-part of copending application Serial No. 133,162 filed on March 26, 1937, for Electrolytic etching machines, which application is a divisional-application of the application Serial No. 79,265 filed by Francis Joseph Brislee and Reginald Blackburn on May 12, 1936, for Electrolytic etching machines. In such processes the plate to be etched forms the anode and the passage of current through the bath takes metal from the anode and liberates it at the cathode. A principal requirement of electrolytic etching is that it should produce a uniform effect on'all parts of the plate. It has been found that there is a tendency to produce more rapid etching near the edges of a Plate than near the centre. There is also the further defect that, in many cases, the etching extends to the back of the plate near the edges. Satisfactory etching apparatus should avoid defects of the kind. indicated and should generally also be capable of dealing with a large range of sizes of plates. These plates are usually flat and rectangular, but they vary in dimensions. The method of operation forming the present invention avoids the defects above indicated and is capable of being embodied-in apparatus which meets the requirements set out above effectively and conveniently.

The invention deals with cases where the cathode is parallel with the anode, i. e., their surfaces are equidistant. Uniformity of etching is obtained by so placing the effective surface of the cathode and making it of such dimensions that the edges of at least two sides thereof, when projected on the anode, lie within the corresponding edge thereof, by a distance dependenton the distance by which the anode and cathode are separated. For instance, with fiat anode and cathode spaced apart vertically by a d stance of fromtwo and a half to three inches, it is found that satisfactory results are obtained if each edge of the cathode lies within the corresponding edge of the anode by a distance of three quarters to one inch. This distance is found to be constant over a large range of sizes and proportions of plates and to be of the order of one quarter to one half cathode when projected on the anode lies within the boundary thereof on three sides only it is found that if the anode plate is turned in its own plane from time to time so that the unmasked edge is moved into a position in which it is opposite to a mask the tendency to produce more rapid etching of the plate on the edge not masked from the cathode does not seriously affect the uniformity of the etching effect on the finished plate. If, however, only two sides of the effective area of the cathode when projected on the anode lie within the boundary thereof, more frequent turning of the plate is found to be necessary. It will be seen that if the anode is maskedon two opposite sides itwill be necessary to turn it through each time it is removed from the bath, but if the masking is on two adjacent sides it will be necessary to turn it through so that the two adjacent unmasked sides take up a position opposite to the masks. The prevention of the etching of the backs of the plates may be obtained by obstructing current from flowing to the back of the cathode.

To provide for the practical requirements of a large range of sizes of anodes, it is preferred to use a large cathode plate and to obtain the required change of dimensions by means of movable vision of fixed masks covering one or more edges of the cathode plate or by so placing and dimensioning the cathode plate that if its area were projected on the anode plate one or more edges of the area so projected would lie inside the boundaries of. the anode plate by the required amount.

In the following paragraphstwo practical embodiments of the method of attaining the object of the invention will be described with the aid of the accompanying drawings.

These drawings show electrolytic etching machines arranged for the etching of flat plates.

Figure 1 is a longitudinal section. of one form of, machine and Figure 2 is a transverse section on the lines II-II of Figure 1.

Figure 3 is a longitudinal section of alternative form of machine, Figure 4 is a transverse section on the line IVIV'of Figure 3 and Figure 5 is a plan View of the alternative form of machine.

The

In both examples a tank l is about two-thirds full of electrolyte, up to the line 2, and has supports for the plate 3 to be etched arranged so as to hold this just below the surface of theelectrolyte.

Where the plate 3 which is being etched is of zinc, it is preferable to make the cathode of zinc. A1l.other parts which are immersed in the electrolyte should be of insulating material. Ifmetal is used, it must be coated with insulating material. For etching copper, it is desirable to have a cathode of steel or iron.

Referring now to the machine shown in Figures l and 2, electrical connection is made with the plate 3 by the contact member 9, which consists of a disc I0, of the same metal as the plate 3, and a casing of insulating material I I, serving as a holder for the disc and the end of the flexible connecting cable l2. The disc [0 is recessed in the centre part'of the lower face. Effective contact is secured by the weight of the contact member. No mechanical connection is made between the contact and the plate, so that the member 9 can readily be lifted away from the plate and replaced as required in the manipulation of the plate during the process of etching.

The cathode 69 is placed at a short distance below the anode and parallel with it. Current is led out of the cathode by the insulated conductor '33, Figure 2. The effective area of the cathode is made less than that of the anode by the use of two movable and two fixed barriers. These enclose a rectangular space of which two adjacent walls are movable, while the other two are fixed so that a large range of dimensions can be given to the effective area of the cathode. It will be seen that the barriers cover a strip along each of the four sides of the cathode and obstruct the flow of current from the anode to the parts of the cathode lying outside the barriers including the back of the cathode.

The whole of the machine is mounted on a frame made of hard wood, which is placed within but not connected with the tank I so that the contents may be lifted completely out of the tank when required. This facilitates the manufacture of the tank of insulating material. It may, for instance,'be made of porcelain. The princi pal members of the frame are four vertical posts 66 carrying two side planks 61 and connected by transverse member 68. The cathode is a flat, unperforated plate 69, mounted between the two side planks 61. On it rests a grid 10. This is a perforated plate of insulating material which lies on the upper face of the cathode and is capable of sliding backwards and forwards on this surface, being actuated by the lever 1|, pivoted at 12 on one of the planks 61. By this reciprocatory movement, the grid can clear the upper face of the cathode of deposits of loose metal or other substances. It is only necessary to move the grid at intervals so as to prevent the deposit becoming excessive.

Near each end of the planks 61 are mounted, in bearings in the planks, two rollers 13, round which passes an endless band of rubber 14, the upper part of which lies upon the grid 10. The movement of the band is brought about by means of the worm and worm wheel, shown as acting upon the right roller in Figure and actuated by a handle 15 on a vertical spindle. The band 14 consists of two substantially equal parts. One of these (shown in the left hand part of Figure 1) extends the full width of the cathode .face of the anode.

forming a continuous cover for that part of the cathode over which it lies. The other part of the band consists of two narrow strips, one at each side. These cover only the extreme edges of the cathode. At the upper end of the full portion of the band is located a stiffening strip 16 which may be of hard rubber, and, immediately behind this strip and near one side of the band, is mounted on the band a vertical peg 11.

Between the planks 51 extends a transverse member 78 which lies near the right hand end of the cathode in Figure 1 and has an inclined projection 19 with a ledge at the upper'end of it. On this ledge rests one edge of the plate 3 to be etched. The projection I9 serves as a barrier and covers a strip of the cathode to the required extent. The upper part of the transverse members 18, which extends above the level 2 of the electrolyte, shields the adjacent edge and back part of the plate from the current. At the opposite edge, the barrier is provided by the band 14 and its stiffening strip 16. This band is adjusted by the handle 15 until the peg 11 comes into contact with an edge of the plate 3.

The other two edges of the plate are supported and shielded as shown in Figure 2. At one side, there is the barrier 80 mounted on one of the planks 61 and projecting forward to the required distance at its lower edge and providing at its upper edge a ledge for the plate to rest on. On the other side is a movable barrier 8| which also has a projecting lower edge and a ledge to receive the plate. This barrier slides across the cathode, being carried at one end on the rod 82 and at the other end on the ledge on the barrier 19.

Means for agitating the electrolyte can be provided, if necessary, either in the lower part or at the ends of the tank. The use of the scraper grid takes the place of a separate agitator to some extent.

The anode and cathode can, with advantage, be made to slope to the horizontal to a slight extent (about one in fifteen). This slope has the effect of assisting the movement of bubbles of gas and particles of solid material across the The sloping can readily be obtained by raising one side or one end of the frame by lengthening the appropriate pair of posts.

In the alternative form of apparatus shown in Figures 3 and 4 and 5 provision is made for supporting the anode plate 3 on two or three sides only. Referring to these figures, the contact member consists of a block 83 of the same metal as the plate 3 mounted on a rod 84, serving also to connect the block 83 with the end of a flexible connecting cable 85. When not in use the contact member is supported on a hook 86. Effective contact is secured by the weight of the contact member, no mechanical connection being made between the block 83 and the plate 3 so that the contact member can readily be lifted away from the plate and replaced as required in the manipulation of the plates during the process of etching.

The cathode 81 consists of a perforated plate which is so supported as to slope to the horizontal to a slight extent (about one in fifteen). The cathode is mounted on a frame made of hard wood which is placed within, but not connected with, tank I so that the contents may be lifted completely out of the tank when required. This facilitates the manufacture of the tank of insulating material, and it may, for instance,'in

the construction being described, be made of por-- celain. The principle members of the frame are four vertical posts 88 connected by transverse members 9| and carrying ebonite sheets 89 and 90 at their upper ends. the cathode 81 is spaced from the adjacent sheet 90 by a distance equal to about one quarter the distance between the anode and cathode. A member 93 for supporting the plate 3 is removably mounted against the endsheet 9|] adjacent to the lower edge of the cathode 81, and similar members 94 are mounted against the side sheets 89. Members 94 carry blocks 95 at their lower edges which act as masks for the cathode 81. The plate is supported on a third side by a crossmember consisting of an ebonite sheet 95 supported vertically on a base 91. The sheet 96 is apertured at 98 and a member 99 extends along the upper edge of the aperture 98 and projects therefrom on both sides to provide ledges for supporting anode plates. The cross-member may be moved from side to side along the tank, so that different sized plates may be treated. The sheet 96 is provided with a rectangular notch which engages with a beading I00 on the upper of the side sheets 90. The base 91 of the cross-member acts as a mask to cover a. strip of the cathode opposite to one edge of the plate 3. It will be seen that the effective area of the oathode, if projected, would lie within the boundary of the plate 3, by an approximately constant distance on three sides, by virtue of the masking effect of the member 91, one of the blocks 95 and the space between the lower edge of the cathode and the side sheet 99.

' From time tctime the plate 3 is removed from the bath and is turned in its own plane before being replaced so that a different edge is ex,-

posed to the cathode.

In this construction more than one plate may be treated at once and for this purpose two contact members are provided and an additional cross-member. In Figure 5 a plate I9! is shown in position supported and masked on one side by the cross-member used for supporting the plate 3 and on the other side by a similar cross-member I02. The plate l0l will need to be turned more frequently than the plate 3 in order to obtain even etching since two of its edges are exposed to the cathode.

Means are provided for agitating the electrolyte in the bath by blowing air into it. Perforated pipes I03 are situated beneath the cathode and mounted between two cross-members I04 which are supported on tlg endtransverse members 9| of the frame work. The air is supplied to the pipes I03 through pipes I05 and the supply is controlled by a valve I06.

It will generally be advantageous to make of rubber each of the faces of the barriers and side planks on which an edge of the'anode plate rests in the construction described, so as to provide. a yielding support ensuring good contact between the plate and the carrier and preventing the lodging of bubbles of gas or particles of solid.

material there.

Instead of the combination of a flexible band and a movable vertical barrier illustrated in Figures 1 and 2, the masking of the cathode can be carried out, as far as the two movable edges of the mask are concerned by using two flexible bands disposed at right angles to each other, each being similar to that shown in the said figures. Many other arrangements for carrying out the invention may also be adopted.

The lower edge 92 of What we claim as our invention is:

1. In a method of etching the surface of a multi-sided flat metal plate electrolytically the step which comprises placing the said surface which forms the anode parallel to a fiat cathode, which cathode has an effective area so placed and dimensioned that the edges of at least two of the sides thereof, when orthogonally projected on to the anode, lie each within the corresponding edge thereof by a distance equal to about one quarter to one half of the distance between the anode and cathode.

2. In a method of etching the surface of a multi-sided fiat metalplate electrolytically the step which comprises placing the said surface, which forms the anode, parallelwith a fiat cathode, which cathode has an eifective area so placed and dimensioned that when this area is orthogonally projected on the anode, it lies with in the boundary thereof by an approximately constant distance on at least three sides, which distance is about one quarter to one half the distance between the anode and cathode.

3. In a method of etching the surface of a multi-sided fiat metal plate electrolytically the step which comprises placing the said surface which forms the anode parallel with a fiat cathode, which cathode has an eifective area so placed and dimensioned that when this area is orthogonally projected on the anode it lies within the boundary thereof by an approximately constant distance on all sides, which distance is about one quarter to one half the distance between the anode and cathode.

, 4. In a method of etching the surface of a multi-sided flat metal plate electrolytically, the steps of placing the said surface, which forms the anode, parallel with a flat cathode, the effective surface of which being so placed and dimensioned that the edges of two sides thereof when orthogonally projected on the anode he each within the corresponding edges thereof by a distance equal to about one quarter to one half the distance between anode and cathode, and removing the plate from the electrolytic bath from time to time and turning it in its own plane before replacing it in the bath.

5. In a method of etching the surface of a multi-sided fiat metal plate electrolytically the steps of placing the said surface, which forms the anode, parallel with a flat cathode, the effective surface of which being so placed and dimensioned that the edges of three sides thereof when orthogonally projected on the anode lie each within the corresponding edges thereof by a distance equal to about one quarter to one half the distance between anode and cathode, and removing the plate from the electrolytic bath from time to time and turning it in its own plane before replacing it in the bath.

6. In a method of etching'the surface of a multi-sided fiat metal plate electrolytically, the steps which comprise etching the said surface which forms the anode by arranging it parallel to a flat cathode in a bath of electrolyte, said cathode having an. effective area which is less than the area of the anode by a marginal strip on at least two sidesof a width equal to about one quarter to one half the distance between the anode and cathode, and removing the plate from the bath from time to time during the etching process,

turning it in its own plane and replacing it in the etching action and in other positions to stronger Y etching action than the central part whereby to equalize the etching action on all parts of the anode.

7. In a method of etching the surface of a metal plate electrolytically the step which comprises placing the said surface which forms the anode parallel with a fiat cathode, which cathode has an efiective area so placed and dimensioned that when this area is orthogonally projected on the anode it lies within the boundary thereof, by an approximately constant distance, which distance varies from about one-fourth to one-half the distance between the anode and the cathode.

FRANCIS JOSEPH BRISLEE. REGINALD BLACKBURN. 

